Because I don't live in Westminster, I don't get to vote in the council elections there. However, because I work there and cycle there, I'm a daily victim of the state of the cycling infrastructure (or lack thereof). What Westminster does (or doesn't) do with its roads system affects the rest of London. Given that we have an elected London Mayor and Assembly, it would seem logical for transport policy to be decided at that level. After all, many journeys cross borough boundaries - that's the nature of travel. Yet Westminster's anti-cycling and pro-car policies largely negate any improvements for cyclists in surrounding boroughs.
I also don't get to vote in the City of London. The City has a literally mediaeval system of governance that bears little resemblance to a democracy. It also has pretty mediaeval cycling infrastructure.
The Westminster and City electorates are not representative of London as a whole so why should they be dictating how London's surface transport should be run? Transport in these two areas has a disproportionately large impact on the functioning of London as a whole. Surely it's time for the roads system in these two areas to form part of a London-wide strategy administered by the London Mayor and Assembly?
(Of course, that would not of itself improve London cycling much as TfL would be in charge, but it would remove one of the obstacles.)